A study on flow characteristics of a thermal expansion circuit breaker near the current zero period

The recent market trend of gas circuit breakers, which have the most important duty to interrupt fault currents in a circuit, is getting more and more small size and low mechanical energy to reduce the cost and increase the reliability. However, the real testing of breakers are rather cost intensive and only demonstrate whether or not a circuit breaker interrupts. Therefore many researches using computational methods have been done for switching arc phenomena and applied to extend the information such as thermal and dielectric recognition. We have simulated switching processes of a thermal expansion circuit breaker that uses the combination of two interruption techniques, the self-expansion by the arc itself and the arc rotation by coils. In order to calculate the governing equations described the dominant physical processes accurately, the commercial CFD code, which is customized to allow the inclusion of arc plasma modeling by Fortran subroutines externally, has been used. Through this work, we have found such information about the thermal performance that the energy produced by the arc causes the pressure-rise in the chamber during high current period. As the current falls near current zero, furthermore, the gas flows back from this region over the arc and should extinguish the arc just after current zero. The results have been compared with various dimensions and verified with the measured arc voltage.